1. Field of the Invention
The present invention relates to an electrical hand-held tool for producing at least a percussion movement, e.g., a hammer drill or chisel hammer with, preferably, a pneumatic percussion mechanism.
2. Description of the Prior Art
Electrical hand-held tools with a pneumatic percussion mechanism are used for generating percussions of a reciprocating oscillation movement which is transmitted to a gas spring arranged between a piston, which is sealingly displaceable in a hollow cylinder relative thereto, and an axially spaced for the piston, sealingly movable percussion means. A rotational movement of an electrical drive is transformed, at least partially, by a suitable transformation gear, primarily by an eccentric oscillator or a wobbling oscillator, in a reciprocating movement of the piston. With a correct use, a counterforce, which acts in the axial direction of the tool, acts, in the path of application of a force (force path), as a reaction percussion or impact via the working tool, the percussion mechanism, the transformation gear and its support on the tool causes application of disturbing vibration to a person who applies the force to the tool.
From the physics of constrained amplitude oscillations of a suspended pendulum, it is basically known that it is possible to effectively dampen particularly high oscillation amplitudes in case of resonance or reverse the oscillation amplitudes by widely spaced from each other, resonant and oscillation frequencies. With the resonant or natural frequency of the suspended pendulum, the oscillating mass and the spring constant which, with a simple percussion, electrical hand-held tool, are defined by the tool mass and the spring constant of the user when the user operates the tool, are dampened. Therefore, a certain oscillation amplitude of the percussion, electrical hand-held tool is determined dependent on the number of percussions that defines the oscillation frequency.
U.S. Pat. No. 3,918,535 discloses arrangement of a preloaded compression spring in the force path between the axially displaceable percussion mechanism and the housing in order to increase the spacing between the operating points. The spring partially oscillatingly decouples the first axially displaceable subassembly, which includes the percussion mechanism, from the second subassembly which includes the housing. Thereby, the relative movement of the first subassembly with respect to the housing, which is caused by the partial oscillating separation of the first and second subassemblies, can be dampen by using a damping element. The resulting system of two decoupled, acting in the same direction, oscillators contains a relatively small mass of the first subassembly, which includes the percussion mechanism, and it is the first subassembly that is subjected to strong oscillations as a result of the recoil of the percussion. The relatively large mass of the second subassembly, which includes the housing, is subjected, dependent on its resonant frequency, only to constrained oscillations with a small oscillation amplitude.
The damping of the recoil energy by a relative movement of the second subassembly using a damping element depends basically on the dissipated portion of the deformation energy of the damping element. The recoil energy damping increases with the increase of the deformation force amplitude and the deformation path amplitude.
U.S. Pat. No. 5,927,407 discloses the use of six elastomeric components for reducing the oscillations of oscillatingly decoupled subassemblies of a hand-held tool. The elastomeric components act in the axial direction, and their viscous elastic energy dissipation is optimized in accordance with the oscillation frequency. The foregoing solution permits to reduce the oscillation amplitude only relatively to the case when a damping element is used.
Accordingly, an object of the present invention is to provide a percussion, electrical hand-held tool having reduced vibrations in comparison with the conventional tools.
Another object of the present invention is to provide a substantially wear-free driving chain between two, movable relatively to each other, vibration decoupled, subassemblies of a percussion, electrical hand-held tool.